what medications are you taking?
i ask because sometimes there can be a drug interaction

what dose of seroquel do you take it and do you take it at night?

if you are switching to zyprexa thats good, zyprexa works well... just be careful not to eat up everything in the fridge

i take zyprexa and seroquel together

i only experienced sleepyness from the seroquel, no cognitive effects besides helping my depression...
i haven't felt any bad effects from zyprexa beside gaining a little weight, zyprexa helps me stay sober... i dont have cravings like i used to....

lithium you need frequent blood testing, becareful with that one

hope you feel better soon, hang in there

PS:
is it possible that you can talk with your father/parents about the fact that you are going to start tapering off seroquel and need them to try to help you through it and be understanding that you may have withdrawal effects?
remember breathing techniques and try to relax yourself when those worries come to you